OBJECTIVE: To identify the optimal intensity and duration of cupping that would minimize mechanical skin deformation.METHODS: We developed an optical measurement probe and system for measuring skin color values in real time. We applied cupping at the following five Bladder Meridian acupoints. To investigate optimal intensity, negative pressure intensity was increased every 2 min up to 80 k Pa. To investigate optimal time, 10 measurement sites were selected and negative pressure intensities of 30, 60, and 80 k Pa were applied for 5 min each. Skin color information was analyzed by the following skin color values: red color saturation, erythema index, and melanin index.RESULTS: The red color saturation and erythema index increased steadily up to 60 kpa negative pressure intensity, then decreased between 60 and 80 k Pa. Therefore, maximal values were observed at 60 k Pa. The melanin index consistently increased with increasing negative pressure intensity. The red color saturation and erythema index did not change after 20 s at 60 k Pa negative pressure intensity. For negative pressure intensities below 80 k Pa, significant changes in melanin index were not observed after 20 s. At 80 k Pa negative pressure intensity, the melanin index exhibited an increasing pattern for200 s, then showed no changes.CONCLUSIONS: To minimize skin deformation, 60 k Pa and 20 s were the appropriate intensity and duration when using red color saturation and erythema index as diagnostic indexes. Because of the increasing pattern up to 80 k Pa negative pressure intensity, the optimal intensity of melanin index could not be determined. When applying 80 k Pa negative pressure intensity and using melanin index as the diagnostic index, we recommend a duration of 200 s.